I think the NSA wanted to give her a secure Windows Mobile (or whatever it was called back then) phone, which may have been better supported. They also mention security issues with Blackberry, presumably even if they tried to make it "secure" themselves.

If I remember correctly, they didn't want to allow Obama to use a Blackberry either back then, but he was a big fan of Blackberries and said he couldn't use the much uglier and brick-like alternatives. So I think they eventually compromised for the president. But I don't think they were just going to do it for everyone else, at least not at the time.